Apparatus for automatic correction of the positioning control of a burner

ABSTRACT

Apparatus for automatically correcting the ratio between the volumetric flows of combustion air and of fuel of a burner comprising an opacimeter which delivers an electric signal proportional to the opacity of the fumes of combustion and a servo mechanism, for example an electric ram controlled by said signal, which automatically varies a dimension, for example the length, of one of the pivoted arms which automatically controls the degree of opening of the combustion air control valve. The apparatus equipped with a reflection opacimeter highly sensitive to fumes which are practically invisible, gives good combustion despite variations of density of the combustion air.

United States Patent Guigues et al. 1 June 4, 1974 1 APPARATUS FORAUTOMATIC 3,549,089 12/1970 Hamlctt 431/12 x CORREQTION OF THEPOSITIONING 3,701,622 10/1972 Ducassc 431/76 CONTROL OF A BURNER l lInventors? FredFl'ic Glllglles, Allee de Primary ExaminerEdward G.Favors Bastlde des Cypres, 13100 Aix-en-Provence; Marcel T. Pillard, 6,Avenue Frederic Mistral, 13008 7 Marseille, both of France [57] ABSTRACT[22] Filed: May 1, 1973 [21] AWL No; 356,230 Apparatus for automaticallycorrecting the ratio between the volumetric flows of combustion air andof fuel of a burner comprising an opacimeter which de- ForeignApplication Priority Data livers an electric signal proportional to theopacity of May 1, 1972 France 72.20971 the fumes of combustion and aservo mechanism, for example an electric ram controlled by said signal,[52] us. Cl. 431/76, 236/15 E, 431/12, which automatically varies a dimnsi for a pl 431/79, 431/90 the length, of one of the pivoted arms whichautomati- [51] Int. Cl. F23h 1/02, F23h 5/08 Cally controls the degreeof opening of the combustion [58] Field of Search 431/12, 79, 76, '90;air control valve. The apparatus equipped with a re- 236/15 E; ZOO/61.03flection opacimeter highly sensitive to fumes which are practicallyinvisible, gives good combustion de- [56] References Cited spitevariations of density of the combustion air.

UNITED STATES PATENTS 3,292,855 12/1964 Wright 431/12 8 Claims, 1Drawing Figure 1 APPARATUS FOR AUTOMATIC CORRECTION OF THE POSITIONINGCONTROL OF A BURNER The present invention relates to an apparatus forautomatic correction, based on the opacity of the fumes, of the ratiobetween the volumetric combustion air flow and the volumetric fuel flowof a burner, which ratio is maintained constant by a positioningcontrol.

The technical field of the invention is that of the constructionofburners for pulverulent, liquid or gaseous fuels and more particularlythe control apparatus with which these burners are fitted.

It is known that it is very important for the ratio between thequantities of fuel and combustion air delivered to a burner to beproperly controlled to prevent the production of fumes.

Prevention of environmental pollution means that constructors must givemore attention to this question.

Burners with a very high heating capacity, which are fitted in certainfurnaces or steam generating boilers for example, are generally providedwith a much improved control sequence known as measuring control,including apparatus for measuring both the fuel flow and the combustionair flow which deliver control signals acting on relays with derived,proportional or integral action, which relays act in turn onservo-motors which control the flow of fuel and the flow of combustionair.

In such control sequences, it is possible to cause correction signals toact on the relays and it has already been proposed to use a signalprovided by an opacimeter, which measures the opacity of the combustionfumes, as a correction signal. Such an opacimeter generally consists ofa photo-electric receiver which picks up a light bundle which has passedthrough the combustion fumes.

A control has also been proposed in which the signal provided by anopacimeter acts on a relay which controls a servo-motor acting on thecombustion air valve. ln such a control, the flow of air is controlleddirectly as a function of the opacity of the fumes and independently ofthe fuel flow.

Such a system is very dangerous in practice, for if a fault occurs inthe control sequence, the burner operates under very bad conditions.

In addition to measuring controls, there exists a large number offire-boxes of medium size, the burners of which are fitted with what isknown as a positioning control.

A positioning control means a control which has means for simultaneouslyvarying the volumetric fuel and combustion air flows, without measuringthese flows, and maintaining a constant ratio between them. Suchapparatus have a pressure or temperature probe situated in the circuitof the hot gases, hot water or steam produced by the apparatus to whichthe burner is fitted, which probe acts on the operating rate of theburner.

They include an air-valve for controlling the combustion air flow, theextent of the opening of which is controlled automatically by motiontransmission apparatus having cams and pivoted arms.

The shape of the cams and/or the lengths of the pivoted arms, whichconsist of rods and levers, are defined experimentally duringcommissioning trials, so that the ratio between the volumetriccombustion air flow distributed by the air valve and the volumetric fuelflow remains constant for all operating rates and equal to the ratiowhich corresponds to the best quality of combustion. Such a positioningcontrol is much less costly than a measuring control sequence, as itrequires only one probe, one relay and mechanical motion transmissions.For this reason it is generally used in fire-boxes having a low ormedium heating capacity.

As opposed to its great simplicity and low installation and upkeepcosts, such a positioning control does not enable a .very goodcombustion quality to be maintained constantly.

In fact this control does not take into account the differences indensity in the combustion air due to temperature variations betweennight and day or between winter and summer, or possible variations inthe temperature, viscosity, calorific power and pressure of the fuel,which result in modifications in the ratio between the mass flow ratesof comburant air and fuel, it being possible for this ratio to departfrom the limits fixed by regulations for preventing pollution of theatmosphere.

It is only necessary to remember the very great influence of variationsin the temperature of the combustion air on the mass flow rate ofcombustion air to appreciate how the combustion quality can vary withsuch a positionih g control apparatus distributing a determinedvolumetric flow of combustion air. ln fact, for a same volumetricair-flow, the mass flow rate exhibits variations of 3.7 percent for atemperature variation of 10C; 7.3 percent for a temperature variation of20C; ll percent for a temperature variation of 30C; 14.6 percent for atemperature variation of 40C and 18.3 percent for a temperaturevariation of 50C.

Temperature variations of the order of 30 between night and day areusual, which fact gives rise to the considerable advantage of theinvention.

The object of the present invention is to automatically correct theratio between the volumetric combustion air flow and the volumetric fuelflow of a burner, which burner has an air-valve for controlling thecombustion air flow, the extent of the opening of which is automaticallycontrolled by a positioning control apparatus having cams and pivotedarms which simultaneously vary the volumetric flows of fuel andcombustion air in a constant ratio.

The solution enabling this object to be achieved consists of providingthe said burner with an opacimeter which delivers an electrical signalproportional to the opacity of the combustion fumes and aservomechanism, controlled by the said electrical signal, whichautomatically varies a dimension of at least one of the said arms.

The said servo-motor preferably consists of an electric ram of variablelength, forming a portion of the length of one of the said arms.

An apparatus in accordance with the invention includes an apparatus formeasuring the electrical signal delivered by the opacimeter, whichapparatus has two adjustable thresholds arranged on either side of amedian position and determines the extension of the ram when one of thethresholds is exceeded and the retraction of the ram when the otherthreshold is exceeded.

A cyclic circuit-breaker is inserted between the said measuringapparatus and the said ram to avoid 0scillations of the ram.

Opacimeters are known which are used as apparatus for measuring theopacity of fumes and which consist of a light source and aphoto-electric receiver which picks up the light bundle emitted by thesaid light source and reflected by the combustion fumes. Such apparatusdeliver an electrical voltage proportional to the opacity of the fumesand they are very sensitive in the almost invisible range of fumeshaving a Bacharach index of less than 5. In accordance'with a feature ofthe invention, such a reflection opacimeter. is used, which offers theadvantage of being able to act on the ratio between the volumetric flowsof combustion air and fuel, while keeping the combustion fumespractically invisible, the Bacharach index of the latter remainingbetween 2 and 4 for example, which corresponds to very good combustion.

When the air-valve for controlling the combustion air flow is wide openor completely closed, action of the servo-mechanism, which could causepermanent distortion of the pivoted arms, must be prevented. This resultis achieved by means of two circuit-breakers on which the air-valve actswhen it reaches its wide open or completely closed positionsrespectively, which circuit-breakers are inserted in the electriccontrol circuits of the said servo-mechanism.

The result of the invention is an apparatus for automatically correctinga positioning control so that the opacity of the fumes always remainsbelow a threshold and is in constant compliance with combustion qualityregulations.

One of the advantages of this apparatus is due to the fact that it actsas a correction apparatus. If a defect occurs in the opacimeter, theboiler continues to function with the non-corrected positioning control.

Another advantage of the apparatus in accordance with the inventionresults from the fact that it can be adapted easily to known controlsand controls which have already been installed.

The following description refers to the attached drawing, which showsschematically and by way of a non-limiting example, an apparatus inaccordance with the invention. 7

The single FIGURE shows a known positioning control consisting of:

l. a probe 1, which measures a value linked to the operation of thefirebox, for example the steam pressure or the water temperature in thecase of a boiler.

2. a regulator 2. This regulator is a relay which makes an analogconversion of the value measured by the probe into a modulated pressurein the case of a pneumatic control sequence, or a modulated voltage inthe case of an electric or electronic control sequence.

3. a relay 3 enabling the operation of the burner to be controlledeither manually or automatically.

4. a motorised valve 4 positioned in conduit 4a which carries fuel tothe burner (not shown).

Valve 4 is a pneumatic valve, for example, opening of which is modulatedby the modulated pressure delivered by regulator 2.

5. a servo-motor 5 which controls the pivoting of a cam 5a.

Servo-motor 5 is a pneumatic ram, for example, movements of which aremodulated in parallel to the opening of valve '4, by the modulatedpressure delivered by regulator 2. e

6. a system of rods and levers ll connecting cam 5a to a mobileair-valve 6 positioned in the combustion air circuit of the burner.

The lever closest to cam 5a has a roller 11a which bears against theoutline of the cam.

Air valve 6 is a double butterfly valve, for example, positioned in theintake or delivery conduit of a fan 6a or an air-flap, or a sleevesliding around air openings cut out of the side wall of the burner.

The above assembly constitutes a positioning control well known to theman of the art and no purpose will be served by describing it in moredetail.

When regulator 2 determines an increase in the fuel flow, i.e. openingof valve 4, it simultaneously determines the pivoting of cam 5a in sucha direction that air-valve 6 opens and the combustion air flow varies inthe same direction as the fuel flow. Conversely, if regulator 2determines a reduction in the fuel flow, the rotation of cam 50 causesan attendant reduction in the air flow by means of rod-system 11.

As a modification, cam 5a could be positioned in the control of valve 4,or the apparatus can have two cams, one in the control of air-valve 5and the other in the control of valve 4. I

in accordance with the invention, on the walls of fume conduit 12 isplaced an opacimeter consisting of a light source 13a and aphoto-electric receiver 13b which picks up a light bundle reflected bythe fumes in the case of the figure.

Reference 7 indicates the opacimeter box containing the electroniccircuitry and possibly the light source and the photo-electric cellconnected to the fume conduit by optical fibres 7a.

In one of rods 11 connecting cam 5a to air-valve 6, is inserted anelectric double-acting ram 10 enabling the length of rod 11 to be variedto lengthen or shorten it in accordance with the direction of rotationof the ram.

This electric ram could be replaced by any equivalent apparatus, such asa pneumatic or hydraulic ram, for example.

lnthe case of an electric ram, the amplified current supplied byopacimeter 7 acts on relays which control the operation of the ram inone direction or the other, depending upon the direction of variation ofthe current.

In normal operation the burner is supplied with a small excess of airwhich leads to practically invisible fumes. If the opacity increases,this signifies that the ratio between the quantities of air and fuel isdecreasing. In this case, the ram acts on the length of rod 11 in thedirection which increases the air flow. If, on the other hand, theopacity of the fumes decreases, this signifies that the air over fuelratio is increasing, and if no correction were made, there would be arisk of reaching an excess of air which would be prejudicial toefficiency.

in this case, ram 10 acts on rod 11 in the opposite direction, i.e. inthe direction which decreases the opening of air-valve 6.

in order that ram 10 should not be acted on continually, in the circuitconnecting opacimeter 7 to ram 10, is inserted an apparatus withadjustable thresholds 8, e.g. an indexed milliammeter, so that while thecurrent delivered by the opacimeter is between the two thresholds, ithas no effect on the ram.

For example, a lower threshold is set corresponding to a Bacharach indexequal to 2, and an upper threshold corresponding to a Bacharach indexequal to 4. It is known that while the opacity of the fumes remainsbetween these two thresholds, the fumes remain practically invisible andcombustion is very good.

The milliammeter can obviously be replaced by threshold relays or anyequivalent electronic comparison apparatus.

References 9a and 9b indicate a double-contact. cyclic circuit-breaker.This can be replaced by a programmer which delivers one or more ramcontrol pulses at each rotation. Oscillations of the ram are avoided bymeans of this cyclic circuit-breaker.

To prevent ram 10 from acting on the rods when airvalve 6 is wide openor completely closed, extreme position circuit-breakers l4, closed bythe air-valve, are employed, which eliminate the action of the ram whenthey are closed.

Of course, without departing from the scope of the invention, variousequivalent modifications could be made by a man skilled in the art tothe apparatus described above.

We claim:

1. Apparatus for automatically correcting the ratio between thevolumetric combustion airflow and the volumetric fuel flow of a burner,including an air-valve for regulating the combustion airflow, the extentof the opening of which valve is controlled automatically by apositioning control device having cams and pivoted arms whichsimultaneously vary the volumetric flows of fuel and combustion air in aconstant ratio, which apparatus includes a reflection opacimetercomprising a light source and a photoelectric receiver sensing a lightbundle emitted by the light source and reflected by the combustionfumes, which opacimeter delivers an electric signal proportional to theopacity of the combustion fumes, and which apparatus includes aservomechanism for automatically varying a dimension of at least one ofthe said arms as a function of the said electric signal.

2. Apparatus for automatically correcting the .ratio between thevolumetric combustion air flow and the volumetric fuel flow of a burner,including an air-valve for regulating the combustion air flow, theextent of the opening of which valve is controlled automatically by apositioning control device having cams and pivoted arms whichsimultaneously vary the volumetric flows of fuel and combustion air in aconstant ratio, which apparatus includes a reflection opacimetercomprising a light source and a photoelectric receiver sensing a lightbundle emitted by the light source and reflected by the combustionfumes, which opacimeter delivers an electric signal proportional to theopacity of the combustion fumes, and which apparatus includes anelectric ram of variable length having two operating directions, whichram forms a portion of the length of one of the said arms, and isoperated by said electric signal.

3. Apparatus for automatically correcting the ratio between thevolumetric combustion air flow and the volumetric fuel flow of a burner,including an air-valve for regulating the combustion air flow, theextent of the opening of which valve is controlled automatically by apositioning control device having cams and pivoted arms whichsimultaneously vary the volumetric flows of fuel and combustion air in aconstant ratio, which apparatus includes an opacimeter which delivers anelectric signal proportional to the opacity of the combustion fumes anda servomechanism for automatically lengthening or shortening of at leastone of the said arms as a function of the said electric signal, whichservomechanism comprises an electric ram of variable length having twooperating directions, forming a portion of the length of one of the saidarms and an apparatus for measuring the said electric signal deliveredby the opacimeter, which apparatus has two adjustable thresholdsarranged on either side of a median position and determines thelengthening of the said ram when one of the thresholds is exceeded andthe shortening of the said ram when the other threshold is exceeded.

4. Apparatus in accordance with claim 3, in which a cyclic circuitbreaker is inserted between the said measuring apparatus and the saidram.

5. Apparatus for automatically correcting the ratio between thevolumetric combustion air flow and the volumetric. fuel flow of aburner, including an air-valve for regulating the combustion air flow,the extent of the opening of which valve is controlled automatically bya positioning control apparatus having cams and pivoted arms whichsimultaneously vary the volumetric flows of fuel and combustion air in aconstant ratio, which apparatus includes an opacimeter which delivers anelectric signal proportional to the opacity of the combustion fumes, anda servomechanism for automatically varying a dimension of at least oneof thesaid arms as a function of the said electrical, Signal, and inwhich the said air-valve for regulating the flow of combustion air hastwo circuit-breakers on which the said air-valve acts when it reachesits wide open or completely closed positions, respectively, whichcircuitbreakers are inserted in the electric control circuitry of thesaid servo-mechanism.

6. Apparatus for automatically correcting the ratio betweenthe'volumetric combustion air flow and the volumetric fuel flow of aburner, including an air-valve for regulating the combustion air flow,the extent of the opening of which valve is controlled automatically bya positioning control device having cams and pivoted arms whichsimultaneously vary the volumetric flows of fuel and combustion air in aconstant ratio, which apparatus includes a reflection opacimetercomprising a light source and a photoelectric receiver sensing a lightbundle emitted by the light source and reflected by the combustionfumes, which opacimeter delivers an electric signal proportional to theopacity of the combustion fumes, and which apparatus includes anelectric ram of variable length having two operating directions, whichram forms a portion of the length of one of said arms and is operated bysaid electric signal, which apparatus includes an apparatus formeasuring the said electric signal delivered by the opacimeter whichmeasuring apparatus has two adjustable thresholds arranged on eitherside of a median position, and determines the extension of the said ramwhen one of the thresholds is exceeded, and the shortening of the saidram when the other threshold is exceeded.

7. Apparatus in accordance with claim 6, in which a cyclic circuitbreaker is inserted between the said measuring apparatus and the saidram.

8. Apparatus for automatically correcting the ratio between thevolumetric combustion air flow and the volumetric fuel flow of a burner,including an air-valve for regulating the combustion air flow, theextent of the opening of which valve is controlled automatically by apositioning control device having cams and pivoted arms whichsimultaneously vary the volumetric flows of fuel and combustion air in aconstant ratio, which source and a photoelectric receiver sensing alight bundle emitted by the light source and reflected by the combustionfumes, which opacimeter delivers an electric signal proportional to theopacity of the combus tion fumes, and which apparatus includes anelectric ram of variable length having two operating directions, whichram? forms a portion of the length of one of said arms, and is operatedby said electric signal, which apparatus includes an apparatus formeasuring the said electric signal delivered by the opacimeter. whichmeathe said ram.

Q 1 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION 3,814,570Dated June 4, 1974 Patent No.

Q Frederic Guigues and Marcel T. Pillard Inventor(s) It is certifiedthat error appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

. Column 7, line 3 after "which" insert apparatus includes a reflectionopacimeter comprising a light 9 Signed and Scaled this eighth Day ofJune 1976 [SEAL] Attest:

RUTH C. MASON C. MARSHALL DANN Arresting Officer (nmmissiuner ofPatvmsand Trademark:

1. Apparatus for automatically correcting the ratio between thevolumetric combustion air flow and the volumetric fuel flow of a burner,including an air-valve for regulating the combustion air flow, theextent of the opening of which valve is controlled automatically by apositioning control device having cams and pivoted arms whichsimultaneously vary the volumetric flows of fuel and combustion air in aconstant ratio, which apparatus includes a reflection opacimetercomprising a light source and a pHotoelectric receiver sensing a lightbundle emitted by the light source and reflected by the combustionfumes, which opacimeter delivers an electric signal proportional to theopacity of the combustion fumes, and which apparatus includes aservomechanism for automatically varying a dimension of at least one ofthe said arms as a function of the said electric signal.
 2. Apparatusfor automatically correcting the ratio between the volumetric combustionair flow and the volumetric fuel flow of a burner, including anair-valve for regulating the combustion air flow, the extent of theopening of which valve is controlled automatically by a positioningcontrol device having cams and pivoted arms which simultaneously varythe volumetric flows of fuel and combustion air in a constant ratio,which apparatus includes a reflection opacimeter comprising a lightsource and a photoelectric receiver sensing a light bundle emitted bythe light source and reflected by the combustion fumes, which opacimeterdelivers an electric signal proportional to the opacity of thecombustion fumes, and which apparatus includes an electric ram ofvariable length having two operating directions, which ram forms aportion of the length of one of the said arms, and is operated by saidelectric signal.
 3. Apparatus for automatically correcting the ratiobetween the volumetric combustion air flow and the volumetric fuel flowof a burner, including an air-valve for regulating the combustion airflow, the extent of the opening of which valve is controlledautomatically by a positioning control device having cams and pivotedarms which simultaneously vary the volumetric flows of fuel andcombustion air in a constant ratio, which apparatus includes anopacimeter which delivers an electric signal proportional to the opacityof the combustion fumes and a servomechanism for automaticallylengthening or shortening of at least one of the said arms as a functionof the said electric signal, which servomechanism comprises an electricram of variable length having two operating directions, forming aportion of the length of one of the said arms and an apparatus formeasuring the said electric signal delivered by the opacimeter, whichapparatus has two adjustable thresholds arranged on either side of amedian position and determines the lengthening of the said ram when oneof the thresholds is exceeded and the shortening of the said ram whenthe other threshold is exceeded.
 4. Apparatus in accordance with claim3, in which a cyclic circuit breaker is inserted between the saidmeasuring apparatus and the said ram.
 5. Apparatus for automaticallycorrecting the ratio between the volumetric combustion air flow and thevolumetric fuel flow of a burner, including an air-valve for regulatingthe combustion air flow, the extent of the opening of which valve iscontrolled automatically by a positioning control apparatus having camsand pivoted arms which simultaneously vary the volumetric flows of fueland combustion air in a constant ratio, which apparatus includes anopacimeter which delivers an electric signal proportional to the opacityof the combustion fumes, and a servomechanism for automatically varyinga dimension of at least one of the said arms as a function of the saidelectrical signal, and in which the said air-valve for regulating theflow of combustion air has two circuit-breakers on which the saidair-valve acts when it reaches its wide open or completely closedpositions, respectively, which circuit-breakers are inserted in theelectric control circuitry of the said servo-mechanism.
 6. Apparatus forautomatically correcting the ratio between the volumetric combustion airflow and the volumetric fuel flow of a burner, including an air-valvefor regulating the combustion air flow, the extent of the opening ofwhich valve is controlled automatically by a positioning control devicehaving cams and pivoted arms which simultaneously vary the volumetricflows of fuel and combustion air in a constant ratio, which apparatusincludes a reflection opacimeter comprising a light source and aphotoelectric receiver sensing a light bundle emitted by the lightsource and reflected by the combustion fumes, which opacimeter deliversan electric signal proportional to the opacity of the combustion fumes,and which apparatus includes an electric ram of variable length havingtwo operating directions, which ram forms a portion of the length of oneof said arms and is operated by said electric signal, which apparatusincludes an apparatus for measuring the said electric signal deliveredby the opacimeter which measuring apparatus has two adjustablethresholds arranged on either side of a median position, and determinesthe extension of the said ram when one of the thresholds is exceeded,and the shortening of the said ram when the other threshold is exceeded.7. Apparatus in accordance with claim 6, in which a cyclic circuitbreaker is inserted between the said measuring apparatus and the saidram.
 8. Apparatus for automatically correcting the ratio between thevolumetric combustion air flow and the volumetric fuel flow of a burner,including an air-valve for regulating the combustion air flow, theextent of the opening of which valve is controlled automatically by apositioning control device having cams and pivoted arms whichsimultaneously vary the volumetric flows of fuel and combustion air in aconstant ratio, which source and a photoelectric receiver sensing alight bundle emitted by the light source and reflected by the combustionfumes, which opacimeter delivers an electric signal proportional to theopacity of the combustion fumes, and which apparatus includes anelectric ram of variable length having two operating directions, whichram forms a portion of the length of one of said arms, and is operatedby said electric signal, which apparatus includes an apparatus formeasuring the said electric signal delivered by the opacimeter, whichmeasuring apparatus has two adjustable thresholds arranged on eitherside of a median position, and determines the extension of the said ramwhen one of the thresholds is exceeded, and the shortening of the saidram when the other threshold is exceeded, in which apparatus the saidair-valve for regulating the flow of combustion air has twocircuit-breakers on which the said air-valve acts when it reaches itswide open or completely closed positions respectively, whichcircuit-breakers are inserted in the electric control circuitry of thesaid ram.